IRON-CATALYZED COUPLING OF TRICYCLO[4.1.0.0(2,7)]HEPT-1-YLMAGNESIUM BROMIDE AND RELATED GRIGNARD-REAGENTS WITH PROPARGYLIC AND ALLYLIC HALIDES

Several uncatalyzed and transition metal-catalyzed cross coupling reactions of the Grignard compounds 1c or 2c with propargylic or allylic halides were investigated. Fe(acac)3 was the most effective catalyst for the preparation of allyl- and propargylbicyclo[1.1.0]butanes 7 and 5. In the latter case, the formation of the isomeric allenylbicyclo[1.1.0]butanes 6 was also observed. Stereoelectronic factors of substituents like a trimethylsilyl group as a directing group could be utilized for the formation of either 5 or 6. A number of bicyclo[1.1.0]butanes 15-21 with two substituents in the bridgehead positions were accessible by that route as well. In the case of the bis-allenyl compound 24c, an ene-type reaction leading to the first known derivative of a [4.1.1]propella-2,4-diene 25 was observed. Base-catalyzed isomerizations of the propargylbicyclo[1.1.0]butanes 5 opened a new route to alkynylbicyclo[1.1.0]butanes 30-32.